Redeposition characteristics of focused ion beam milling for nanofabrication

In this article, a new method is presented to measure the focused ion beam induced sputter distribution, obtained with 30 keV Ga+ ions. Small holes with diameters ranging from 400 to 1750 nm have been created in a lamella with a thickness of approximately 300 nm. Short ion beam pulses sputter small amounts of material from the bottom of the hole that redeposit at the opposite side. Assuming axial spatial symmetry, imaging the hole before and after redeposition yields a quantitative cross section of the sputter distribution. It has been found that at low ion currents (< 6 pA) and low ion dose (< 10(+8)) the method produces reliable, reproducible results for 30 keV Ga+ ions on silicon. The method is compared with SRIM simulations in Si and with previously published results. The simulated and measured results are in good agreement. At the higher dose/current regime, small Ga droplets are formed, probably as a result of sputtered Ga dopants in Si. As a result of this, the method becomes less accurate and the simulation is no longer valid due to the fact that the substrate milling has to include the many Ga dopants to a certain depth. (c) 2007 American Vacuum Society.